Biomes

Boreal Forest

Dense forests of coniferous evergreens along the northern edge of the temperate zone make up this biome. Winters are dangerously cold, but summers are mild and long enough to allow the ground to thaw. The word for this biome comes from the Greek word for "north", reflecting the fact that this biome occurs mostly in the northern part of the northern hemisphere.

Temperate Woodland and Shrubland

In this biome, large areas of grasses and wildflowers such as poppies are interspersed with oak and other trees. Communities that are more shrubland than forest are known as chaparral. Dense low plants that contain flammable oils make fire a constant threat.

Northwestern Coniferous Forest

Mild moist air from the Pacific Ocean influenced by the Rocky Mountains provides abundant rainfall to this biome. It includes a variety of conifers, from giant redwoods to spruce, fir, and hemlock, along with flowering trees and shrubs such as dogwood and rhododendron. Moss often covers tree turnks and the forest floor. Because of its lush vegetation, this biome is sometimes called a "temperate rain forest."

Tropical Dry Forest

This biome growss in areas where rainy seasons alternate with dry seasons. In most places, a period of rain is followed by a prolonged period of drought.

Desert

This biome has less than 25 centimeters of precipitation annually, but otherwise vary greatly, depending on elevation and latitude. Many of these areas undergo extreme daily temperature changes, alternating between hot and cold.

Tundra

This biome is characterized by permafrost, a layer of permanently frozen subsoil. During the short cool summer, the ground thaws to a depth of a few centimeters and becomes soggy. In winter, the top layer freezes again. This cycle of thawing and freezing, which rips and crushes plant roots, is one reason that tundra plants are small and stunted. Cold temperatures, high winds, a short growing season, and humus-poor soils also limit plant height.

Tropical Rain Forest

This biome is home to more species than all other biomes combined. It gets at least 2 meters of rainfall per year. Tall trees form a dense, leafy covering called a canopy from 50-80 meters above the forest floor. In the shade below the canopy, shorter trees and vines form a layer called the understory. Organic material on the forest floor is recycled and reused so quickly that the soil in most tropical rain forests is not very rich in nutrients.

Temperate Forest

This biome is mostly made up of deciduous and evergreeen coniferous trees. Coniferous trees, or conifers, produce seed-bearing cones, and most have leaves shaped like needles, which are coated in a wazy substance that helps reduce water loss. These forests have cold winters. In autumn, deciduous trees shed their leaves. In the spring, small plants burst from the ground and flower. Fertile soils are often rich in humus, a material formed from decaying leaves and other organic matter.

Tropical Grassland/Savanna/Shrubland

This biome receives more seasonal rainfall than deserts but less than tropical dry forests. Grassy areas are spotted with isolated trees and small groves of trees and shrubs. Compacted soils, fairly frequent fires, and the action of large animals - for example, rhinoceroses and elephants - prevent some areas from turning into dry forest.

Temperate Grassland

This biome, underlain by fertile soils, once covered vast areas of the midwestern and central United States. Periodic fires and heavy grazing by herbivores maintained plant communities dominated by grasses. Today, most have been converted for agriculture because their soil is so rich in nutrients and is ideal for growing crops.